During the years 1967 and 1968 some data were obtained on the
life history and behavior of Ornithoptera alexandrae Rothschild, the largest known
species of Rhopalocera. The geographic distribution of O. alexandrae is limited
to a relatively small area in southeastern Papua New Guinea. However, within
its range, there are many areas where the butterfly does not occur although the
host plant grows prolifically.
The main habitat is a low and relatively flat region, but it has
also been observed at altitudes up to 900 mete: O. alexandrae is monophagous.
Its hostplant is Aristolochia schlechteri, a vine having rather large, thick
leaves and stringy stems covered with a layer of strongly ribbed cork.
The flower is shaped like a starfish with three long arms and is
dark purple-brown with a yellow heart. ‘The fruit is green, shaped like a small
cucumber 20 to 30 cm long, strongly ribbed longitudinally and has a rough skin.
It matures slowly and when fully rotten the seeds fall to the ground and are
carried away by rainwater generally over short distances, resulting in a number
of plants growing in a restricted area.
In primary forest the vine reaches the top of tall trees of over
40 meters high. When larvae were transferred to Aristolochia tagala, a plant
more generally distributed, it was accepted readily and the larvae developed
normally, although at a much faster rate than larvae feeding on their natural
host. Data recorded show a rapid growth as v with larvae of Papilioaegeus when
reared on parsley or carrot leaves instead of their natural food plants.
When
three larvae, obtained from eggs collected in the field, were reared on A.
tagala they went through six instars instead of the usual five. It is not known
whether this is hereditary or environ- as the case mental, The female butterfly
does not oviposit on A. tagala. Oviposition.
Generally a single egg is laid on
the under surface of an old leaf of the hostplant. In secondary forest where
this plant is not ver tall, the egg is laid from a few centimeters above the
ground to about one meter above it. On several occasions a female was observed
laying on other objects than the food plant such as a grass stem growing at a
dis- tance of a few centimeters from one of the main stems of the Aristolochia
vine. In primary forest, however, oviposition may take place at a con-
siderable height above the ground.
Egg. Large, light yellow, flattened at the
base, Diameter 34% mm. Covered with a thick layer of a bright-orange sticky
substance, which fixes it firmly to the surface ‘on which it is laid.
Incubation period varying from 11 to 13 days. First-instar Larva. Ground colour
dark wine red. All segments with long tubercles of same colour as body;
tubercles fleshy for about one-fourth their length, remain- ing part stiff and
black with numerous black spines.
Two dorsal tubercles on the fourth abdominal
segment light red as is dorsal saddle mark joining them on the same segment.
Saddle mark divided mid-dorsally by a narrow black line. Head, prothoracie
shield and legs black; prolegs dark, fleshy. Newly hatched larva seven to eight
mm long. Osmaterium orange yellow. Second-instar Larva, Ground colour reddish
black. Tubercles proportionately longer, all fleshy and without spines,
latero-dorsal ones the longest.
Dorsal and latero-dorsal tubercles on thoracic
segments two and three, and dorsal ones on ab- dominal segments one, seven,
eight and nine red; two dorsal tubercles on ab- dominal segment four
creamy-white with pink tips; remaining tubercles of ground colour, First
thoracic segment with four tubercles, following three segments with eight;
abdominal segments two to eight with six; ninth abdominal with four and the
last segment with two tubercles, Third- to final-instar Larvae, Ground colour
unchanged, ‘Tubercles without spines, of nearly equal length except for the
ventro-lateral ones which are very short, In ultimate instar, body tubercles
proportionately smaller than in early instars, All bright red except two dorsal
ones on fourth abdominal segment which remain creamy white with pink tips.
Conspicuous saddle mark extending and narrowing down to spiracles. Some larvae
with an additional creamy spot on third abdominal segment. Measurements of a
large, mature larva: length 118 mm, greatest width 30 mm; headcapsule length,
12 mm, width 11 mm; longest tubercle, 13 mm. Some larvae have six instars instead
of the usual five, and these producing the largest butterflies.
Adult. The size
of the butterfly varies considerably. The average length of the forewing in the
male is 97 to 100 mm, in the female 118 to 126 mm. Many specimens are smaller,
few are larger. One previously unrecorded feature is that some males have
translucent, yellow discal spots on the hind wings, homologous to those of
priamus and victoriae.
In the higher altitudes of its range the total figure
may reach 180 days depending on the locality. It was observed that larvae
feeding on Aristolochia schlechteri spend much time in search of suitable
leaves and stems. However, those feed- ing on the succulent and soft parts of
Aristolochia tagala rarely move around and appear to have a longer average
daily feeding time. Feeding habits. Shortly after hatching the larva devours
its eggshell, which provides sufficient food for the next 24 hours.
It then
commences. Later instars feed on older leaves and stems. Fifth and sixth
instar larvae feed mainly on the stringy feeding on tender shoots and young
leavi stems and shortly before pupation one or more stems of the host vine are
severed, causing the upper parts to wither. If the plant is young, the lower
part is eaten down to the ground. Pupation. The larva may wander for 24 hours
or longer to locate a suitable site for pupation, which sometimes occurs at a
considerable distance from where it was feeding last.
The longest recorded
distance was nearly 10 meters. It generally pupates under a leaf of any kind of
shrub or tree other than the hostplant, rarely on stems, at an average height
of one to two meters above the ground in secondary forest, but considerably
higher in primary forest. Pupa.
The ground color is light brown. Wing cases are yellow, with a
broad light-brown streak along the lower margin. Abdomi its brown ventrally and
yellow dorsally, with a yellow latero-ventral. streak. I saddle mark bright
yellow, extending over segments one to five. Middorsally divided by a narrow
dark brown line; a similar line running laterally below wing cases, ‘Thorax
dark brown, tegulae bright yellow. Abdominal segments five to eight with two
very short, sharp, black processes each. Pupa very closely resembles that of
O. victoria. Duration of the pupal stage from forty to forty-five days. General
observations. Female butterflies appear to follow a determined flight pattern
when ovipositing.
This is suggested by the fact that larvae in different stages
of development, together with one or more pupae or exuviae, may always be
located on or near the same foodplant, while other plants growing in the
vicinity remain free of specimens the year round. It is possible that females,
in their search for suitable conditions for oviposition, are stimulated by
plants that already do support or have previously supported early stages.
Single larvae are only found on small plants. Although it has not been possible
to determine the longevity of the adults it is believed to be similar to that
of O. priamus. Some males of Alexandria were clearly marked after they emerged
from the pupa and then released in a garden. A few of these specimens
established themselves for the duration of their adult life in the same
garden, where both hostplants and flowers were prolific. After 11 weeks, one
male was found caught in a large spiderweb.
Another died in the same way after
nearly 12 weeks. Predators and diseases. Several larvae have been found marked
with numerous rust-brown dots, sitting motionless without feeding. They died
after several weeks and may have been killed by a fungus disease. On one
occasion a larva covered with eggs of a Tachinid was collected, but continued
feeding pupated normally, and produced the adult. Apparently, the parasite
eggs did not hatch or the resulting maggots did not survive.
A native collector
once had a pupa that produced a large number of small, black wasps, probably
Chalcididae. Otherwise, larvae of O. alexandrae are rarely attacked by
parasites. Prepupae and soft, fresh pupae are sometimes killed by ants and
wasps and mature larvae and pupae are attacked by tree rats and small
marsupials, When not mating both sexes may be seen, generally flying high
(average 20 to 30 meters above the ground) and in a single direction. In the
forest, males are seldom seen as they remain in the shade of the high canopy
and avoid open or exposed areas. Fecundity. Two females were taken on the wing
while ovipositing. Both specimens appeared in good condition, but it was
impossible to make an accurate estimate of their age. They were kept alive and
fed daily se and honey solution.
After 12 days in captivity, both specimens were
killed. One female had laid one egg; dissection of its abdomen produced another
16 mature eggs. On the basis that not more than 10 eggs had been laid before
its capture, we can estimate a total capacity of 25 to 27 eggs. Dissection of
the second female produced a total of 12 eggs of which two were immature. as
